This invention relates to novel means for improving the quality of sound or image to be reproduced and, more particularly, to specifically configured sheet members which are adapted to be adhesively attached to stringed musical instruments, loudspeakers, compact discs, laser discs or the like to improve their acoustic or imaging performance. Further, the invention relates to the formation in compact discs, laser discs, magnetic tapes, semiconductor chips, circuit boards, magnetic or IC cards or the like of a plurality of cut-outs so configured to reduce the interference caused by electromagnetic radiations therefrom.